Telephone repeater station



March 1, 1927. 1,619,058

G. cRlssoN TELEPHONE REPEATER STATION Filed Feb. '7, 192

[ 2 v -INVEN'T'OR; 7 w 6'. 622129013 BY W ATTORNEY rammed Mar. 1, 1927.

GEORGE CRISSON,

OF HACKENSACK; NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TELEPHONE REPEATER STATION.

Application filed February 7, 1922. Serial No. 534,721.

This invention relates to arrangements for establishing a three-waytelephone connection at a repeater station. With the arrangements of theinvention, three-way com- 6 munication may be established between thetwo ends of a long telephone line and one or more intermediate stations,such as repeater stations, in connection with demonstrations of longdistance telephony or in 1v connection with the distribution of publicspeeches in which at one or more points on a line it may be desirable topermit audiences to hear speech coming from a single point and which mayat the same time permit talking into the line from these variousstations. The invention might find further application in other fields,such as on leased wire telephone lines in which service is to bedistributed to a number of stations along the line in a manner to permitany one station to talk to any other station. The arrangements mightalso be utilized for monitoring purposes where it is desirable for thesupervisor to talk into the line as well as to listen on the line.

The arrangements of the invention pro- -vide novel means for connectingtalking and listening loops to a through telephone line wherebyprovision may be made for talking with equal volume in each directionfrom the repeater on the through line, or, if desired, with any givendifference in volume in the two directions; for listening with equalefliciency to the conversation in either direction over the through lineor with any desired efficiency in either direction; for unimpairedtransmission through the repeater of conversation between the terminalsof the line; and for an adjustable volume or side tone in the receivingloop. Other'features and advantages of the invention will appear morefully from the detailed description hereinafter given.

The invention may be more fully understood from the followingdescription together'wit-h the accompanying drawing, in the Figure 1 ofwhich is illustrated a circuit diagram embodying the principles ofthe-invention and in the Fig. 2 of which is shown a'modificationthereof.

- In Fig. 1 is shown a conventional form of two-way two-element repeaterinterconnecting the two line sections L and L This repeater may beeither of the cord circuit type or the through-line type and ineludesthe usual net works N L and N for balancing the lines L and L thethreewinding transformers 1. and 2, the vacuum tube elements 3 and 5 andother appa ratus, such as the filter 4 and (3. Connected with the inputcircuits of the tubes 3 and 5, by means of the circuits 17 and 18, is atalking circuit L, to which may be connected talking apparatus. Thetalking circuit L includes the potentiometer 7, the transformer 8, avacuum tube amplifier 9, the series resistance elements 10, 11 and 12,the transformers 13, 14 and 15. The resistance 12 is provided with anadjustable contact 16 so that it can function as a potentiometer. Theresistance elements 10 and 11 are arranged in a manner similar to 12.Associated with transformer 15 is a side-tone circuit 19, which will hemore fully described later. Bridged across the network conductors of therepeater are the circuits 23 and 25. These circuitsare connected throughthe transformers 20 and 21 to a receiving circuit L which may includetelephone receiving apparatus. This receiving circuit also includes thevacuum tube amplifier 22. The side tone circuit 19 is associated withthe input circuit of the tube 22.

Transmission between the lines L, and L takes place in the usual mannerand without interference from any of the added apparatus.

When it is desired to talk from the line L over the lines L and L thevoice currents arriving over line L enter potentiometer 7, the drop inwhich is stepped up by the input transformer 8 and applied to the vacuumtube 9 in the usual manner. The output current of the vacuum tubetraverses the resistances 10,11 and 12 in series. Transformers 13 and 14transfer the voltages across the resistances 10 and ll to the two gridcircuits of the vacuum tubes 3 and 5 of the line repeater to send speechcurrents in each direction through the line. Due to the very highgrid-filament impedance of the vacuum tubes 3 and 5, no currents ofappreciable magnitude are caused to flow in the grid circuits, and nointerference between the two sides of the repeater occurs;

The volume of speech currents repeated from the talking loop L, to thethrough line depends upon the design of the apparatus associated withline L 1 It can be adjusted by means of the potentiometer 7 is usuallythe case, it is desired to send equal speech currents in both directionsfrom the repeater, the resistances 10 and 11 are equal, and transformers13 and 14 have the same ratio. In this case a single resistance and asingle transformer with two equal secondary windings could be usedinstead of'the arrangement shown. By giving r unequal values to theresistances 10 and 11,

or by using transformers of different ratio, the speech currentstransmitted in the two directions from the repeater may be made todiffer from each other by any desired ratio. If the speech currents inthe talking i circuit L are strong enough, it is possible to dispensewith the amplifier 9 and transmit the currents directly to theresistances 10, 11 and 12. i

The operation of the arrangements in receiving voice currents coming inover the lines L or L is as follows: If voice currents arrive over thethrough line, for example, from the line L little or none of thedisturbance will reach the network N and the input transformers 20 ofthe listening circuit will be substantially unaffected. The speechcurrents will be amplified by the line repeater 3 and transmitted to theline L and the network N The'voltage set up across the'ter'mina-ls ofthe network N is impressed upon the primary winding of the inputtransformer 21 of the listening amplifier 22. This transformer steps thevoltage up or down as may be necessary and impresses it upon the grid ofthe vacuum tube 22 of the listening amplifier, which repeats the speechcurrents into the listening circuit L in the usual-manner. Speechcurrents from the section L of the through line reach the listeningcircuit L in the same way, except that the input transformer 20transfers the voltage across the network N, to the grid of the vacuumtube 22, while transformer 21 is unaffected. By this arrangement, theeffects produced in the listening circuit L depend only on the outputvoltage of the line repeater. If the transformers 20 and 21 wereconnected across the line terminals of the line repeater, it willreadily be seen that both the input and output voltages of the linerepeater would act in producing speech currents in the listening circuitL and the resulting current would be the sum or difference of thecurrents, due to the input and output voltages of the repeaterconsidered separately, depending upon the arrangement of the transformerconnections. This would'lead to some uncertainty as to the volume of thespeech currentsin the lis- When, as

toning circuit L and probably would cause distortion of these currents.These effects would become more harmful as the gain of the line repeateris reduced.

Ordinarily the two transformers 20 and 21 would have equal turn ratios,in order that the listening circuit L would receive with equalefiiciency the speech passing in either direction through the linerepeater. By using transformers having different ratios, or by makingthe ratio of one or both transformers adjustable, the receivingefficiency could be made different for transmission in the twodirections over the through line. This would make is possible tocompensate for differences in the transmission level in the twodirections and so cause each terminal of the line to .be heard L,. Thehigh impedance of the grid circuit .of the "acuum tube 22 insures thatthere will be no interference between the two sides of the line repeaterthrough the trans formers 20 and .21. The primary windingsoftransformers 20 and 21 are wound to such high impedance that they donot appreciably affect the balance of the line repeater.

When speech currents reach the transmit produced by speech'between theends of the through line. To overcome this effect, con

motions of the transformers 20 "and 21 are so arranged that the voltagesof their secondary windings caused by speech, currents from the talkingcircuit L oppose each other, and little or no current is produced in thelistening circuit L,. In order that person listening to the receivingapparatus connected with circuit L may hear what is said on the talkingcircuit L the side-tone circuit 19 is provided. This consists of thepotentiometer device 12 previously mentioned and a transformer 15 whoseprimary winding has impressed upon it an adjustable voltage from thepotentiometerand whose secondary winding is connected in"ser ies withthe secondaries of the input trans formers 20 and 21 to the grid of thevacuum tube 22. Speech currents in the talking circuit L thus producespeech currents in the listening circuit L whose volume can be adjustedby means of the potentiometer contact 16 to be equal to'that receivedfrom the through line, or to'any other desired value.

similar reference characters are used to denote like parts with respectto Fig. 1. The supervisory apparatus is denoted as X and may includeboth talking and listening apparatus. The talking apparatus will beconnected in substantially the same manner as in Fig.1 by the circuit Lto the circuits 17 and 18"which are connected in series .in the gridcircuits of the tubes 3 and 5. A relay 51 controlled by switching means'K at the set X is provided whcreby'the talking set at X may beoperatively disconnected from circuits 17 and 18 when desired. Thelistening circuits 23 and :25 are connected to line L and thence to theapparatusat X.

The listening circuits 23 and 25 are coupledto the lines L and L in adifferent manner than in Fig. 1 being related inductively thereto byadditional windings on the hybrid coils 2 and 1. As the operation wouldbe substantially similar to the arrangements H of Fig. 1 no furtherdescription thereof will be given.

While the invention has been disclosed as embodying certain specificarrangements which are deemed desirable, it is understood that itiscapable of embodiment in many and widely varied forms withoutdeparting I from the spirit and scope of the appended claims.

What is claimed is:

1. In combination with a transmission. line includin a two-way repeaterand networks for ba ancing the sections of the lines interconnected bythe repeater, a listening circuit, and circuits bridged across theterminals of the networks associated with the line sections forassociating said listening circuit with said repeater.

2. In combination with a transmission line including a two-way repeaterand networks for balancing the sections-of the lines interconnected bythe repeater, a listening circuit having a vacuum tube included therein,and circuits bridged across the terminals of the networks associatedwiththe'line sections for associating said listening circuit with saidrepeater.

3. In a transmission system including a two-wa vacuum. tube repeater andnetworks or balancing the sections of the lines interconnected by therepeater, a talking I circuit, a transformer having a plurality ofsecondary windings, the primary windings of said transformer beingconnected to said talking circuit and the secondary wmdmgs a pluralityof windings,

of said transformer being connected in series in the grid circuits ofsaid vacuum tubes, a listening circuit, and circuits bridged across theterminals of the networks associated with the line sections forassociat-- ing said listening circuit with said repeater. 4. In atransmission system including a two-way vacuum tube repeater andnetworks for balancing the sections of the lines interconnccted by therepeater, a talking circuit, a transformer having a plurality ofwindings, the primary windings of said transformer being connected tosaid talking circuit and two of the secondary windings being connectedin series in the grid circuits of sai vacuum tubes. a listening circuitincluding a vacuum tube amplifier, circuits bridged across the terminalsof the networks as'sociated with the line sections for associating saidlistening circuit with said repeater,an a slde tone circuitmterconnectmg said talking and listening circuits, said side tonecircuit being connected in series in the grid circuit of said amplifierin said listeningcircuit and being inductively related to said talkingcircuit.

5. In a transmission system including a two-way vacuum tube repeater, atalking circuit including a otentiometer, an amplifier, a plurality ofresistance elements. in series in said circuit, transformer windings inparallel withsaid resistances, and secondary windings inductivelyrelated to said first mentioned transformer windings, said secondarywindings being included in series in the grid circuits of said vacuumtubes.

6. In a transmission system a two-way repeater comprising two one-wayvacuum tubes for a talking circuit, and a transformer having the primarywindings of said transformer being connected to said talking circuit andthe secondary windings of said transformer being connected the inputcircuits of respectively in series in the vacuum tubes of said repeater.I

7. In a transmission ,system a two-way repeater, a talking circuit,transformers having their primary windings connected to said talkingcircuit, the secondary windings ofsaid transformers being connectedrespectively in series in the input c rcuits of said repeater wherebytransmisslon ma take place from said talking circuit simu taneously over.both of the line sections interconnected by said repeater, and meansfor adjusting the volume. of transmission from said talking circuit tosaid line sections, said means comprising lndividual variable resistanceelements connected 1n said talking circuit in parallel with each of theprimary windings of said transformers.

8. In a transmisslon system including a two-way vacuum tube repeater andnetworks transmission in opposite directions, 7

dividual transformers with theirsecondary windings in series in the gridcircuit of said amplifier, the primary windings of said transformersbeing. bridged across the terminals of the networks associated with saidline sections, and means for varying the condition of said transformer-.windings whereby the volume of transmission from 1 either of said linesections to said listening circuit may be independently adjusted. y

In testimony whereof I have signed my name to this specification this4th day of February, 1922. a

- GEORGE CRISSON.

